Question

A force of 600 N elongates a spring from its natural length of 18 cm to a length of 20 cm. What is the work done?

(a) 116J

(b) 114J

(c) 118J

(d) 120J

I have been asked this question during an interview for a job.

This key question is from Work Done by a Variable Force topic in division Work, Energy and Power of Physics – Class 11

Answer 1

The correct choice is (b) 114J

The best explanation: The force on a spring stretched by x meters is given by F = k*x where k is the spring constant. So, 600 = k*(2/100). Now k = 3*10^4, and hence F = 30000*x. W = \(\int_{x1}^{x2}\)F * dx = \(\int_{0.18}^{0.2}\)30000 * x * dx = 114 J.